S-band EPR spectra on a synthetic mimic of the mixed valence [CuA(1.5) CuA(1.5)], S = 1/2 EPR-detectable site in nitrous oxide reductase, N2OR, and cytochrome c oxidase, COX, were obtained. Also, X-band spectra were obtained to ensure that the sample was not altered upon changing EPR tubes. Previously accumulated X-band spectra from N2OR and COX were sent to Minnesota group for comparison with the spectra for the synthetic model.